Advanced Feed System for Semi Solid Casting

ABSTRACT

A feed system for introducing semi-solid metal alloy to a die casting machine includes a first chamber for receiving a metal alloy billet and for preparing the semi-solid metal alloy billet. The first chamber includes heaters and a cutting system. The metal alloy billet is heated by the heaters and cut by the cutting system into predetermined lengths to form semi-solid metal alloy portions. The feed system also includes a second chamber connected to the first chamber by a passage to receive the semi-solid metal alloy portions. The second chamber includes a door that opens and closes the passage and a plunger system that introduces the semi-solid metal portions to a die cast machine. An atmosphere control system is in fluid communication with the first chamber and the second chamber. The atmosphere control system removes oxygen from the feed system. A method using the feed system is also provided.

The present invention relates to methods for metal casting, andparticularly feed systems and methods for semi-solid metal (SSM) castingparts.

BACKGROUND OF THE INVENTION

Semi-solid metal (SSM) casting, also known as semi-solid forming, is ahybrid manufacturing method that incorporates elements of both castingand forging. Semi-solid metal casting (SSM) is a near net shape variantof die casting. Die casting is a popular metal forming technique forforming metal or metal alloy parts. Die casting finds broad applicationin diverse technologies such as automotive parts, plane parts, toys,utensils, and the like. In the typical die casting process, a moltenmetal or metal alloy is forced under high pressure into a mold cavity.

Unlike typical die casting, SSM process is to introduce raw materialswith nondendritic microstructure in the semi-solid state. SSM is done ata temperature that puts the metal between its liquidus and solidustemperature. Ideally, the metal should be 30 to 65% solid. The metalmust have a low viscosity to be usable, and to reach this low viscositythe material needs a globular primary surrounded by the liquid phase.The temperature range possible depends on the material and for aluminumalloys is 5-10° C., but for narrow melting range copper alloys can beonly several tenths of a degree.

Semi-solid metal (SSM) casting is typically used for high-end castingswith non-ferrous metals, such as aluminum, copper, and magnesium. Foraluminum alloys typical parts include engine suspension mounts, airmanifold sensor harness, engine blocks and oil pump filter housing.

In SSM process, the metal is usually prepared for introduction into adie cast machine by cutting a metal or metal alloy billet intopredefined lengths and widths. The feedstock is then heated up into thesemi-solid state and introduced into the casting machine. Since themetal is typically heated in ambient before being placed in the castingmachine, the metal (surface) is subject to oxygen contamination oftenwith a layer of oxide forming on the metal portions. Such contaminationcan degrade the quality of the parts being formed resulting inperformance problems.

Accordingly, the present invention provides improved methods of makinghigh quality semi-solid metal castings with the proposed advanced feedsystem and methods of making

SUMMARY OF THE INVENTION

The present invention solves one or more problems of the prior art byproviding, in at least one embodiment, a feed system for semi-solidmetal casting. The feed system includes a first chamber for receiving ametal alloy billet. The first chamber includes heaters and a cuttingsystem. The metal alloy billet is heated by the heaters and cut by thecutting system into predetermined lengths to form semi-solid metal alloyportions. The feed system also includes a second chamber connected tothe first chamber by a passage to receive the semi-solid metal alloyportions. The second chamber includes a door that opens and closes thepassage and a plunger system that introduces the semi-solid metalportions to a die cast machine. An atmosphere control system is in fluidcommunication with the first chamber and the second chamber. Theatmosphere control system removes oxygen from the feed system.

In another embodiment, a feed system for semi-solid metal casting isprovided. The feed system includes a first chamber for receiving a metalalloy billet. The first chamber also includes heaters and a cuttingsystem. The metal alloy billet is heated by the heaters and cut by thecutting system into predetermined lengths to form semi-solid metalportions. A second chamber is connected to the first chamber by apassage. The second chamber includes a door that opens and closes thepassage and a plunger system that introduces the semi-solid metalportions to a die cast machine. A gas purging system is in fluidcommunication with and provides a positive pressure of an inert gas tothe first chamber and second chamber.

In another embodiment, a method of feeding metal alloy billet to a diecast machine using the feed systems set forth above is provided. Themethod includes a step of introducing the alloy billet into a firstchamber which has heaters and a cutting system. The alloy billet isheated in a first chamber under a substantially oxygen free environmentto a temperature at which the alloy billet is a semi-solid. The alloybillet is then cut in the first chamber into semi-solid metal alloyportions having a predetermined length. The semi-solid metal alloyportions are introduced into a second chamber through a passage betweenthe first and the second chamber. The second chamber includes a doorthat opens and closes the passage and a plunger system. The semi-solidmetal alloy portions are introduced into the die cast machine by theplunger system.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will become more fullyunderstood from the detailed description and the accompanying drawings,wherein:

FIG. 1 provides a schematic illustration of a feed system for feedingsemi-solid metal or metal alloy to a die casting machine; and

FIGS. 2A, 2B, and 2C provide a schematic flowchart of a method offeeding semi-solid metal alloy to a die casting machine using the systemof FIG. 1.

DESCRIPTION OF THE INVENTION

Reference will now be made in detail to presently preferredcompositions, embodiments and methods of the present invention, whichconstitute the best modes of practicing the invention presently known tothe inventors. The Figures are not necessarily to scale. However, it isto be understood that the disclosed embodiments are merely exemplary ofthe invention that may be embodied in various and alternative forms.Therefore, specific details disclosed herein are not to be interpretedas limiting, but merely as a representative basis for any aspect of theinvention and/or as a representative basis for teaching one skilled inthe art to variously employ the present invention.

Except in the examples, or where otherwise expressly indicated, allnumerical quantities in this description indicating amounts of materialor conditions of reaction and/or use are to be understood as modified bythe word “about” in describing the broadest scope of the invention.Practice within the numerical limits stated is generally preferred.Also, unless expressly stated to the contrary: percent, “parts of,” andratio values are by weight; the description of a group or class ofmaterials as suitable or preferred for a given purpose in connectionwith the invention implies that mixtures of any two or more of themembers of the group or class are equally suitable or preferred;description of constituents in chemical terms refers to the constituentsat the time of addition to any combination specified in the description,and does not necessarily preclude chemical interactions among theconstituents of a mixture once mixed; the first definition of an acronymor other abbreviation applies to all subsequent uses herein of the sameabbreviation and applies mutatis mutandis to normal grammaticalvariations of the initially defined abbreviation; and, unless expresslystated to the contrary, measurement of a property is determined by thesame technique as previously or later referenced for the same property.

It is also to be understood that this invention is not limited to thespecific embodiments and methods described below, as specific componentsand/or conditions may, of course, vary. Furthermore, the terminologyused herein is used only for the purpose of describing particularembodiments of the present invention and is not intended to be limitingin any way.

It must also be noted that, as used in the specification and theappended claims, the singular form “a,” “an,” and “the” comprise pluralreferents unless the context clearly indicates otherwise. For example,reference to a component in the singular is intended to comprise aplurality of components.

Throughout this application, where publications are referenced, thedisclosures of these publications in their entireties are herebyincorporated by reference into this application to more fully describethe state of the art to which this invention pertains.

The term “billet” as used herein refers to a raw metal stock such as abar stock. Therefore, a metal alloy billet is a metal alloy bar stock.

With reference to FIG. 1, a schematic illustration of a feed system forfeeding semi-solid metal or metal alloy to a die casting machine isprovided. Feed system 10 introduces metal alloy billet into die castingmachine 12. Feed system 10 includes first chamber 14 that receives metalalloy billet 16 into receiving section 18. In a refinement, metal alloy16 is manually introduced into first chamber 14. In another refinement,metal alloy billet 16 is provided to first chamber 14 by motorized drivesystem 20. First chamber 14 also includes heaters 22 and cutting system24. Metal alloy billet 16 is heated by heaters 22 to a sufficienttemperature so that the billet becomes semi-solid. Metal alloy billet 16is cut by cutting system 24 into predetermined lengths to formsemi-solid metal alloy portions. The lengths that are cut are chosen toprovide sufficient material for a part that is to be formed in die castsystem 12. The semi-solid metal alloy portions are received into thetransfer section of chamber 14. Feed system 10 also includes secondchamber 28 connected to first chamber 14 by passage 30. Second chamber28 includes door 32 that opens and closes passage 30. Second chamber 28also includes plunger system 36 which introduces the semi-solid metalportions to die cast machine 12.

Still referring to FIG. 1, atmosphere control system 40 is in fluidcommunication with first chamber 14 and second chamber 28. Atmospherecontrol system 40 removes oxygen from the feed system. In a refinement,atmosphere control system 40 is an inert gas purging system thatintroduces an inert gas into the first chamber via inlet port 42.Typically, the inert gas is then introduced into the second chamber viapassage 30. Examples of suitable inert gases include nitrogen, helium,argon and the like. In another refinement, atmosphere control system 40is a vacuum system that excludes oxygen by maintaining feed system 10 atreduced pressure. Optional controller 41 may be used to control both theheaters and atmosphere control system 40.

Still referring to FIG. 1, plunger system 36 includes plunger 44 thatpushes the semi-solid metal portions into die cast machine 12. Plunger36 is positionable in a first position P1 such that the second chamberreceives the semi-molten metal portion and in a second position P2 inwhich door 32 is closed. In the specific variation illustrated in FIG.1, plunger system 36 further includes sheath 46 that operates as door 32by moving with plunger 44. In this variation, section 48 of sheath 46blocks passage 30 when plunger 42 is at position P2 while when atposition P1, passage 30 is open. In a refinement, plunger system 36further includes a biasing member such as spring 50 that contacts thesheath and acts to provide a biasing force that acts to moves sheath 46towards die cast machine 12. In a refinement, plunger system 30 furtherincludes hydraulic system 52 for moving the plunger between positions P1and P2.

With reference to FIGS. 1 and 2A-C, a method of feeding metal alloy to adie cast machine is provided. FIGS. 2A-C provide a schematic flowchartof the method. Feed system 10 receives an alloy billet 16 into firstchamber 14 as set forth in step a). In particular, alloy billet 16 isreceived into receiving section 18. As set forth above, first chamber 12includes heaters 22 and cutting system 24. In step b), alloy billet 16is heated in the first chamber 16 under a substantially oxygen freeenvironment to a temperature at which the alloy billet 16 is asemi-solid which is identified by item number 16′ in FIG. 2A. Oxygen isexcluded by the atmosphere control system by either inert gas purging orby maintaining the first chamber 14 under a vacuum. In step c), alloybillet 16 is cut in the first chamber 14 into semi-solid metal alloyportions 56 having a predetermined length. In step d), the semi-solidmetal alloy portions 56 are introduced into (e.g., transported to) thesecond chamber 28 through passage 30 between the first and the secondchambers. It should be appreciated that plunger 44 is positioned atposition P1 so that passage 30 is open and one of the semi-solid metalalloy portions 56 can enter the second chamber 28. In step e), plunger44 is moved to position P2 causing section 48 of sheath 46 to blockpassage 30. In step f), plunger 44 is moved further along direction d₁so that one of the semi-solid metal alloy portions 56 is introduced intodie casting machine 12. In step g), plunger 30 returns to position P1 sothat another semi-solid metal alloy portion may be transported to thesecond chamber 28.

As set forth above, the variations and embodiments of the feed systemand related method are used to introduce alloys into a die castingsystem. In a refinement, the metal alloy billets include an alloy with afreezing range (between liquidus and solidus). The presence of afreezing range will typically mean that the purely liquid and solidphases do not concurrently exist within this range. In a furtherrefinement the freezing range is from about 5 to about 100 degrees C.,depending alloy compositions. In another refinement, the metal alloybillet comprises an aluminum alloy. Such aluminum alloys typicallyinclude aluminum and a component selected from the group consisting ofcopper, magnesium, manganese, silicon, zinc, and combinations. In suchaluminum alloys, the amount of aluminum is from about 80 weight percentto about 99.95 weight percent and the amount of other alloying elementsis from about 0.05 to about 20 weight percent. In many aluminum alloys,the amount of aluminum is less than about 99 weight percent. Many castaluminum alloys are hypoeutectic alloys having aluminum dendritic phaseforming first during solidification. For example, one type of usefulaluminum alloy includes aluminum and silicon. In such alloys, the amountof silicon is usually from about 4 to 14 weight % with the balance beingaluminum (86 to 96 weight percent) or aluminum plus other alloyingelements (0.05 to 20 weight percent) as above. In another refinement,the alloy billet comprises a component selected from the groupconsisting of magnesium alloys, tin alloys, zinc alloys, and copperalloys.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A feed system for semi-solid metal casting, the system comprising: afirst chamber for receiving a metal alloy billet, the first chamberincluding heaters and a cutting system, the metal alloy billet beingheated by the heaters and cut by the cutting system into predeterminedlengths to form semi-solid metal alloy portions; a second chamberconnected to the first chamber by a passage to receive the semi-solidmetal alloy portions, the second chamber including a door that opens andcloses the passage and a plunger system that introduces the semi-solidmetal portions to a die cast machine; and an atmosphere control systemfor removing oxygen from the feed system, the atmosphere control systembeing in fluid communication with the first chamber and the secondchamber, the atmosphere control system including an inert gas purgingsystem that introduces an inert gas into the first chamber via inletport and then into the second chamber via the passage.
 2. The feedsystem of claim 1 wherein the plunger system includes a plunger thatpushes the semi-solid metal into the die cast machine.
 3. The feedsystem of claim 2 wherein the plunger is positionable in a firstposition such that the second chamber receives the semi-solid metal anda second position in which the door is closed.
 4. The feed system ofclaim 3 wherein the plunger system further includes a sheath thatoperates as the door, the sheath moving with the plunger.
 5. The feedsystem of claim 4 wherein the plunger system further includes a biasingmember that acts to move the sheath towards the die cast machine.
 6. Thefeed system of claim 3 wherein the plunger system further includes ahydraulic system for moving the plunger.
 7. (canceled)
 8. The feedsystem of claim 1 wherein inert gas is introduced into the secondchamber.
 9. The feed system of claim 1 wherein the metal alloy billetcomprises an alloy with a freezing range.
 10. The feed system of claim 1wherein the metal alloy billet comprises an aluminum alloy.
 11. The feedsystem of claim 10 wherein the aluminum alloy comprises aluminum and acomponent selected from the group consisting of copper, magnesium,manganese, silicon, zinc, and combinations.
 12. The feed system of claim10 wherein the aluminum alloy comprises aluminum and silicon.
 13. Thefeed system of claim 10 wherein the metal alloy billet comprises acomponent selected from the group consisting of magnesium alloys, tinalloys, zinc alloys, and copper alloys.
 14. A feed system for semi-solidmetal casting, the system comprising: a first chamber for receiving analloy billet, the first chamber including heaters and a cutting system,wherein the alloy billet is heated by the heaters and cut by the cuttingsystem into predetermined lengths to form semi-solid metal portions, agas purging system providing a positive pressure of an inert gas to thefirst chamber; and a second chamber connected to the first chamber by apassage, the second chamber including a door that opens and closes thepassage and a plunger system that introduces the semi-solid metalportions to a die cast machine.
 15. A method of feeding alloy billet toa die cast machine, the method comprising: introducing the alloy billetinto a first chamber including heaters and a cutting system; heating thealloy billet in a first chamber under a substantially oxygen freeenvironment to a temperature at which the alloy billet is a semi-solid;cutting the alloy billet in the first chamber into semi-solid metalalloy portions having a predetermined length; introducing the semi-solidmetal alloy portions into a second chamber through a passage between thefirst and second chamber, the second chamber including a door that opensand closes the passage and a plunger system; and introducing thesemi-solid metal alloy portions into the die cast machine by the plungersystem.
 16. The method of claim 15 wherein inert gas is introduced intothe second chamber.
 17. The method of claim 15 wherein the alloy billetcomprises an alloy with a freezing range.
 18. The method of claim 17wherein the alloy billet comprises an aluminum alloy.
 19. The method ofclaim 18 wherein the aluminum alloy comprises aluminum and a componentselected from the group consisting of copper, magnesium, manganese,silicon, zinc, and combinations.
 20. The method of claim 18 wherein thealuminum alloy comprises aluminum and silicon.